CVE-2025-0684 is a vulnerability identified in the GRUB2 bootloader, specifically within its reiserfs filesystem module. The flaw occurs during symlink lookups on reiserfs filesystems, where GRUB2 uses user-controlled parameters derived from the filesystem geometry to calculate internal buffer sizes. Due to insufficient integer overflow checks, these calculations can overflow, causing grub_malloc() to allocate a smaller buffer than intended. Subsequently, the grub_reiserfs_read_symlink() function calls grub_reiserfs_read_real() with an overflown length parameter, resulting in a heap-based out-of-bounds write during data reading. This memory corruption can overwrite critical internal GRUB data structures, potentially enabling an attacker to execute arbitrary code at boot time. Such exploitation could bypass secure boot protections, undermining system integrity from the earliest stage of system startup. The vulnerability requires local high-privilege access (e.g., root) to mount or manipulate a maliciously crafted reiserfs filesystem. No user interaction is needed, but the attack vector is limited to systems using GRUB2 with reiserfs support. The CVSS 3.1 score is 6.4 (medium), reflecting the complexity of exploitation and the requirement for high privileges. No known public exploits are reported yet, but the impact on confidentiality, integrity, and availability is high if exploited.

For European organizations, the impact of CVE-2025-0684 can be significant in environments where GRUB2 is deployed with reiserfs filesystems, particularly in legacy or specialized Linux systems. Successful exploitation allows attackers to execute arbitrary code during the boot process, effectively compromising the entire system before the operating system loads. This can lead to persistent backdoors, bypass of secure boot mechanisms, and full system compromise. Critical infrastructure sectors such as energy, finance, and government that rely on Linux servers with GRUB2 may face risks of data breaches, service disruptions, and loss of system integrity. Although exploitation requires local high privileges, insider threats or attackers who gain initial access could leverage this vulnerability to escalate control. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers often develop exploits post-disclosure. The vulnerability also poses challenges for incident response and recovery, as compromised bootloaders can evade traditional detection methods.

1. Apply security patches or updates from GRUB2 maintainers as soon as they become available to address the integer overflow and buffer allocation issues in the reiserfs module. 2. Where possible, avoid using the reiserfs filesystem, especially on systems where security is critical, and migrate data to more widely supported and actively maintained filesystems like ext4 or XFS. 3. Implement strict access controls to limit local high-privilege access, reducing the risk of attackers manipulating filesystem structures. 4. Employ secure boot configurations and hardware root of trust features to detect unauthorized bootloader modifications, although this vulnerability can bypass secure boot, layered protections may help. 5. Use runtime memory protection techniques such as heap canaries and address space layout randomization (ASLR) to mitigate exploitation impact. 6. Monitor system integrity and bootloader configurations regularly to detect anomalies. 7. Educate system administrators about the risks of using legacy filesystems and the importance of timely patching.